PURPOSE: To prepare a high-purity etherified polyoxyalkylene compound, by flocculating colloidal inorganic salt crystal of by-product in a crude reaction solution to form large flocs, separating economically the inorganic salt form the crude reaction solution efficiently.

CONSTITUTION: A polyoxyalkylene compound shown by the formula (R1 is H or residue of organic hydroxy compound containing 1W8C hydroxyl group; m is 1W 500; n is 1W8) is reacted with an alkali metal or an alkali metal compound to give an alcoholate of a polyoxyalkylene compound, which is reacted with an organic halide. The prepared reaction mixture is blended with water, the inorganic salt prepared as by-product in the reaction is removed by solid-liquid separation. An amount of water added is 0.1W10wt% based on the reaction mixture, and the blending is preferably carried out by keeping the reaction mixture at 10W150°C.